Operative viva

Question 1

Talk me through the approach to an anterior circulation aneurysm.

Answer 1

In an appropriately consented patient under GA, I would place the patient supine on the operative table with the head turned to the contralateral side in a Mayfield clamp. PCom = 30 deg MCA = 45 deg ACom 60 deg The malar eminence is at the highest point. Before starting I would ensure I have 1) a microscope available with ICG capability, 2) a Doppler probe and 3) an array of aneurysm clips available. Pterional incision from the zygoma to the widow’s peak behind the hair line. Reflection of a myocutaneous flap. Burr holes at McCarty’s keyhole and above the zygoma. Craniotomy. The greater wing of the sphenoid is drilled down until flush with the anterior cranial fossa floor. A myocutaneous flap is raised prior to a C-shaped durotomy Subfrontal retraction to identify the olfactory nerve, which is followed back to the optic nerve and carotid artery. I would allow CSF egress from the optico-cartoid cistern and then gain proximal control. The ICA can then be followed to the artery.

Question 2

How do you perform a transcallosal approach for a colloid cyst?

Answer 2

In an appropriately consented patient under GA, I would place the patient supine on the operative table with the head neutral in a Mayfield clamp. I would raise the head of the bed to 30 deg. I would utilise image guidance to I perform a souttar incision and place burr holes on either side of the midline 4cm anterior to the coronal suture and 2 cm behind. The craniotomy is carried 5 cm lateral. The dura is reflected over the midline taking care to preserve any cortical and bridging veins. Interhemispheric sharp arachnoid dissection is performed and the calloso-marginal arteries and cingulate gyri are encountered at the bottom edge of the falx. The dissection is continued between the cingulate gyri to the corpus callosum. The pericallosal arteries are identified and a 2 cm transection of the callosum is performed. Orientation within the ventricle is achieved by following the choroid plexus and thalamostriate veins to the foramen of monroe. Transforaminal approach is preferred and can be expanded through the transchoroidal or interforniceal routes. The colloid cysts should be aspirated and released from the tela choroidae. Care should be taken to prevent release of the contents into the CSF potentially resulting in a chemical meningitis.

Question 3

What syndrome is characterised by visual loss and opthalmoplegia?

Answer 3

Orbital apex syndrome

Question 4

Describe a transphenoidal approach.

Answer 4

In an appropriately consented patient under GA, I would place the patient supine on the operative table with the head in a Mayfield clamp. I would rotate laterally flex the head at facilitate access to the nostrils. I would utilise neuronavigation. A lumbar drain is placed for macroadenomas with significant suprasellar extension or for extended cases. I would instil Moffatt’s solution (Cocaine 10% 1ml + Adrenaline 1ml 1:1000 + Bicarbonate. 2ml 8.4%) and prepare the abdomen or thigh for a fat graft. A direct endoscopic approach is performed with lateralisation of the middle turbinate and identification of the sphenoid ostium. A nasoseptal flap may be raised for extended procedures. The bony septum (vomer) is disarticulated from sphenoid rostrum. The sphenoid sinus is entered and the septations are removed. The optic nerve, OCR, carotid arteries and sellar are then identified. The sella then drilled and the dura opened in a cruciate fashion. Suction, angled ring curettes and biopsy forceps are used to deliver the tumour. Valsalva or aliquots of saline can be added to the lumbar drain to aid with delivering suprasellar portions.

Question 5

What is Moffatt’s solution?

Answer 5

Moffatt’s solution = Cocaine 10% 1ml + Adrenaline 1ml 1:1000 + Bicarbonate. 2ml 8.4%

Question 6

What are the complications of a transsphenoidal approach?

Answer 6

Epistaxis (sphenopalatine artery) CSF leak = rhinorrhea Sinusitis Visual impairment Addisonian crisis DI Endocrinopathy Meningitis Opthalmoplegia (Cavenous sinus) Carotid injury

Question 7

Why is a CT helpful for transsphenoidal cases?

Answer 7

Neuronavigation Identify the nasal anatomy Identify the sellar type (sellar, pre-sellar and conchal) Sphenoid septations may lead to the carotid canal

Question 8

What do headaches and visual deterioration suggest?

Answer 8

Raised ICP. This may be due to hydrocephalus, tumours, trauma, venous outflow obstruction etc

Question 9

Describe an ETV.

Answer 9

In an appropriately consented patient under GA, I would place the patient supine on the operative table with the head in a Mayfield clamp. I would utilise neuronavigation and plan a trajectory from a pre-coronal burr hole 3cm from the midline passing through the foramen of monroe to the tuber cenereum in the midline. I would perform a C-shaped incision, single burr hole hole and insert a peel-away cathter (14 French) into the lateral ventricle. I would insert the rigid endoscope, obtain orientation within the ventricle utilising the choroid plexus, septum and thalamostriate veins guiding me to the foramen of monroe. I would fenestrate the floor of the third ventricle at the tuber cenerem between the mamillary bodies and the infundibular recess and dilate this using a 4Fr fogarty catheter with 0.2ml of air. I would advance the endoscope into the prepontine cistern and inspect for any remnant of Lillequists membrane. I would leave an EVD or access device if there was significant bleeding. I would then perform a biopsy of a lesion at this stage if required.

Question 10

What are the imaging features indicative of hydrocephalus?

Answer 10

Evan’s ratio >0.3 (FH:BPD) Bicaudate ratio >0.25 FH:Internal skull dia ratio >0.5 Temporal horns 2 mm Ballooning of the third ventricle Thin / stretched CC Periventricular oedema Empty sella Dilated optic nerve sheath diameters

Question 11

What is the ETV success score?

Answer 11

This is a predictive score of the failure rate of ETV (based on the likelihood of needing a VP shunt @6 month). Predictive factors include: Age (<1 month = 0, 1-6 months = 10, 6-12 months = 30, 1-10 years = 40 and >10 years = 50). Aetiology (Infection = 0, MMC/IVH/tumour = 20 and Aqueduct stenosis = 30). Previous infection (No = 10). Maximum score is 90%.

Question 12

What is the cause of chronic neck pain and occipital headaches worse with coughing / sneezing / valsalva?

Answer 12

Chiari type 1 malformation

Question 13

How would you perform an FMD?

Answer 13

In an appropriately consented patient under GA, I would place the patient prone on a Montreal mattress in the Concorde position with the head in a Mayfield clamp taking care to avoid overflexion and ensuring no obstruction to venous outflow. I would perform a linear incision from inion to C2 with bilateral muscle strip and exposure of the C1 lamina. I would perform a suboccipital craniectomy (3x3 cm) and potentially remove the arch of C1. Y-shaped opening of the dura. If this restores flow across the CCJ then I would perform an expansion duroplasty using autologous pericranium or a dural patch (DuraGuard = Bovine pericardium / DuraRepair = horse Achilles tendon) and multilayered closure. If the tonsils are very low and CSF across the CCJ is not restored then I would undertake tonsillopexy taking care to preserve the PICA.

Question 14

What are the causes occipital headaches and numbness / tingling in the fingers? Long tract signs?

Answer 14

Syrinx and FM tumour / CCJ compression

Question 15

What approach would you use for a ventrolateral foramen magnum meningioma?

Answer 15

Far lateral approach

In an appropriately consented patient under GA, I would place the patient in the park bench position on the operative table with the head in a Mayfield clamp. I would utilise neuronavigation and mark a mitre incision (inverted hockey stick) extending from C3 up to the inion in the midline, along the superior nuchal line to the tip of the mastoid process.

The myocutaneous flap would be elevated and retracted inferiorly and laterally.

The C1 lamina, vertebral artery and lateral mass are identified. The foramen magum is opened.

The vertebral artery can be transposed to facilitate drilling of the occipital condyle (<1/3) to prevent instability.

Curvilinear dural opening.

Question 16

How do you perform a middle fossa approach? e.g. to a petroclival meningioma

Answer 16

Subtemporal transtentorial approach

In an appropriately consented patient under GA, I would place the patient in the park bench position on the operative table with the head elevated 30 deg in a Mayfield clamp. I would utilise neuronavigation and mark an incision from zygoma to 2 cm behind the mastoid curving posteriorly over the pinna.

A low temporal cranitiomy is performed at the floor of the temporal fossa.

Extradural dissection is peformed with coagulation of the MMA, peeling from posterior to anterior to prevent traction on the GSPN.

The arcuate eminance is identified and driling of Kawase’s triangle is performed.

The dura is opened in a T-shape with one limb parallel to the inferior temporal lobe and the other perpendicular along the floor of the temporal fossa.

The CN4 should be identified and protected prior to division of the Sup. Petrosal Sinus.

Question 17

How would you perform a retrosigmoid approach?

Answer 17

In an appropriately consented patient under GA, I would place the patient in the park bench position on the operative table with the head elevated 30 deg in a Mayfield clamp.

I would perform a curvilinear incision 2 finger-breadths behind the ear and place a burr hole 1cm medial and inferior to the asterion.

I would reflect the dural leaflets over the transverse and sigmoid sinuses.

I would drain CSF to relax the cerebellum and then gently place a fixed retractor on the superior surface of the cerebellum (for TN MVD) or lateral cerebellum for VS / HFS MVD. Further CSF can be drained from the foramen magnum.

I would be mindful to prevent avulsion of Dandy’s vein (aka superior petrosal vein).

Question 18

What is the safest way to identify and preserve the CN7/8 with large VS?

Answer 18

Identify the nerves at the exit from the brainstem and roll the tumour laterally.

Question 19

Label the anatomy of the CP angle.

Answer 19

Question 20

How is facial nerve monitoring performed during Vestibular Schwannoma surgery?

Answer 20

EMG electrodes are placed in the orbicularis oculi and oris muscles as well as a ground electrode on the forehead.

Free running EMG and direct stimulation is performed.

A concentric bipolar electrode probe is used starting with a stimulation intensity of 0.05 mA building up in 0.02 mA steps until a response is received. Square wave pulse at 5Hz.

Elevation of stimulation >0.3mA correlates with a poor post-operative facial nerve function.

Question 21

How are brainstem auditory evoked potentials recorded?

Answer 21

An ear mould is placed in the ipsilateral EAC to deliver click noises.

The responses are measured by electrode montages from A1 (anterior to the tragus) with bipolar montage to Cz.

Responses = ECOLI!!

Question 22

How do you perform an ACDF?

Answer 22

In an appropriately consented patient under GA, I would place the patient supine on the operative table with the head on a ring. I would place a roll under the neck/shoulders taking care not to hyperextend the neck and I would tape the chin and shoulders.

I undertake a pre-operative xray for level marking and perform a transverse skin crease incision.

I raise a subplatysmal flap and continue my dissection at the medial border of SCM identifying the carotid sheath and retracting it laterally.

Omohyoid may be encountered and can be mobilised or divided as required

The prevertebral fascia is opened longitudinally and longus coli are retracted laterally.

Caspar pins are inserted under II guidance and distracted. A superficial discectomy is peformed with a currettes using the uncovertebral joints as the lateral margins.

Posterior osteophytes are removed with a high speed drill and the PLL is opened to reveal the dura.

The cartilagenous endplates are removed and a cage with bone graft (autologous from osteophytes or synthetic) is inserted (14 mm depth and 14-18 mm width).

The retractors are removed and a drain is placed on gravity.

Question 23

What are the complications of an ACDF?

Answer 23

Bleeding - neck haematoma / airway obstruction

Infection - potentially requiring hardware removal

Hoarse voice - recurrent laryngeal nerve palsy (20% transient, 4% permanent)

Dysphagia

Oesophagal injury

Tracheal injury

Horner’s syndrome

Spinal cord or root injury injury - Paralysis, bowel / bladder dysfunction, sensory loss and loss of hand function

Delayed C5 root palsy

Adjacent level disease

Hardware failure / subsidence / failure to fuse

Question 24

What proportion of disc prolapses occurs in the thoracic spine?

Answer 24

<1%

Question 25

Where are thoracic disc prolapses most likely to occur?

Answer 25

Below T8 (as the thoracic spine is more mobile)

Question 26

What is the most common site for a thoracic disc prolapse?

Answer 26

T11/12

Question 27

How would you investigate a thoracic disc prolapse?

Answer 27

MRI CT - as frequently calcified (2/3) \*\*Always use IONM\*\*

Question 28

What are the approaches to thoracic disc prolapses

Answer 28

1. Costotransversectomy 2. Lateral extracavitatory (retropleural) 3. Transthoracic approach - has the best operative results and lowest results of injury. Left sided approach avoids the SVC / IVC and hemiazygous / azygous. Right sided approach avoids the artery of Adamkiewicz, heart and aorta.

Question 29

What does a costotransversectomy involve?

Answer 29

Resection of the TP and 5 cm of rib. Disruption of the segmental / spinal artery results in cord ischaemia! Risk of pneumothorax.

Question 30

Where does the artery of Adamkiewicz arise?

Answer 30

Between T8-L1 and from the left side in 80%.

Question 31

Describe a transthoracic approach to a discectomy.

Answer 31

After consent and GA with a double-lumen ET tube, the patient is placed in a lateral position with the right side up (unless it is low thoracic then use the left side as the IVC is difficult to mobilise on the right). Intraoperative neurophysiological monitoring would be instituted throughout the case. Lateral Xray for level check (as a radiologist to put cement into the VB below) A thoracic surgeon is employed to aid with the approach. A rib is resected (one or two above the disc for removal to allow direct lateral access to the disc), pleura opened and the lung is deflated. The intercostal neurovascular bundle is used to guide the surgeon to the neural foramen. Trenches are drilled into the posterior VB above and below the disc. The disc is then dissected into the trench away from the cord without manipulating the cord. The rib can be used as an autologous bone graft and a plate is placed between the VBs.

Question 32

What is the difference between a transthoracic and retropleural approach?

Answer 32

The retropleural approach does not open the parietal pleura and retracts the parietal pleural forwards after opening the endothoracic fascia giving the same access as a transthoracic approach. A chest drain is needed for a transthoracic approach as both the parietal and visceral pleura are opened. For a retropleural approach in which only the endothoracic fascia is opened then only a wound drain is placed.

Question 33

How do you perform a far lateral discectomy?

Answer 33

In an appropriately consented and anaesthetised patient, I would position them prone on the Montreal mattress and undertake an x-ray for the level check. I would utilise a Wiltse approach and make a paramedian incision on the ipsilateral side 3 cm from the midline. I would find the intervening fascia between multifidus and longissimus and dissect down the plane to the facet joint and TP. Internal xray is used to confirm the level again. The intertransverse ligament is incised and using a microscope the neural foramen is identified with the exiting nerve root underneath the pars.

Question 34

Label the thoracic vertebra

Answer 34

Question 35

Label the lumbar vertebra

Answer 35

Question 36

How do you perform a lumbar pedicle screw fixation?

Answer 36

Pre-operatively I would measure the diameter and length of the screws on the CT. I would then position an appropriately consented and anaesthetised patient prone on a montreal mattress and undertake an external level check prior to a midline incision and bilateral muscles strip. I take another internal Xray for level check and identify the superior articular facet, the pars and the TP to identify the screw entry point. I would then used a sharp awl and pedicle finder and place the screw. Medial lateral angulation is based on the level increasing at 5 deg interval from L1 = 5 deg, L2 = 10 deg, L3 = 15 deg, L4 = 20 deg, L5 = 25 deg and S1 = 30 deg. The facet joints are decorticated and bone graft is placed in the gutters. Autologous bone graft or synthetic (DBX = demineralised bone matrix from cadaveric source) The screws are connected to rods and final tightened.

Question 37

What is a lumbar infusion study?

Answer 37

Used to investigate NPH and shunt valve function and is based on the principle that the CSF absorption rate varies with ICP. One or two needles are inserted into the CSF space and the CSF pressure is measured as the baseline in the lateral decubitus position. Hartmann's solution is infused at a steady rate starting at 1ml/min through one needle and the pressure is measured constantly through the other needle until a steady-state plateau pressure is achieved (at least 45 minutes). This indicates the pressure level at which the absorption rate is equal to the infusion rate. A resistance to infusion (R out) \>18 mmHg/ml/min is indicative of shunt response in NPH. If testing shunt function, the peak pressure is the opening pressure of the valve.

Question 38

How do you perform a percutaneous trigeminal rhizotomy?

Answer 38

The symptomatic side is marked and the patient is placed under GA with an LMA in a supine position. Hartel's technique is used to anatomically place the needle into the foramen of Ovale with an entry point 2.5 cm from the corner of the mouth aiming for a target point at the intersection of lines at the mid pupillary line and a point 3 cm anterior to the tragus. Local anaesthesia in placed into the cheek and a finger is placed into the mouth to prevent transgression of the oral mucosa. To confirm the position, CSF is liberated and 1 ml of Iodinated water-soluble contrast agent (Iohexol) can be used to perform trigeminal cisternography. During RF ablation the patient is woken up and then stimulation is performed to reproduce the pain.

Question 39

What RF stimulation settings do you use?

Answer 39

0.2-0.6V aiming for a probe temperature of 70 deg for 60 seconds. High stimulation settings \>0.8V mean the needle needs repositioning. After the RF ablation, the patient is woken up and the amount of anaesthesia in the V1-3 is measured. The ablation is repeated after repositioning if sufficient hypoaesthesia is not achieved.

Question 40

What are the complications associated with poor needle placement?

Answer 40

1. Carotid injury / intracavernous injury 2. IOF (Blindness and opthalmoplegia) 3. Jugular foramen (Lower cranial nerve injury)

Question 41

What are the results of TN procedures?

Answer 41

Initial response: MVD 98%, RF 98%, Balloon 93%, Glycerol 91% Recurrence rates MVD 15%, RF 20%, Balloon 21%, Glycerol 50% Facial numbess MVD 2%, RF 98%, Balloon 72%, Glycerol 60% \*\*All procedures have a \>90% chance of improving pain but the recurrence rate is greatest with glycerol, as is the risk of anaesthesia dolorosa and corneal numbess,

Question 42

What do you aim on xray for the different trigeminal divisions during a percutaneous ablation procedure?

Answer 42

5 mm below the sella = V1 10 mm below the sella = V2 15 mm below the sell = V3

Question 43

What do you send a CSF sample for?

Answer 43

Microscopy for gram stain and cell count, Culture & Sensitivity Biochemistry - glucose and protein paired to serum

Question 44

Describe insertion of a VP shunt.

Answer 44

In accordance with the local shunt protocol, would place an appropriately consented and anaesthetised patient in the supine position with the head turned to the contralateral side. I would register the neuronavigation if being used and plan a suitable trajectory. I would then pre-assemble the reservoir, shunt and distal tubing before placing a c-shaped incision at Keen's point (4cm above and behind the pinna) followed by a burr hole. I would then open the peritoneum through an ipsilateral hypochondrial incision. I tunnel from the cranial incision to the abdomen incision with a trochar. Prior to handling the shunt valve and tubing, I would then change my gloves and pass the tubing through the tunneller prior to removing the tunneller. I would then cannulate the ventricle, cut the proximal tubing to the desired length and connect it to the pre-assembled reservoir/valve/distal tubing. I would check for flow at the distal end before implanting it into the abdomen.

Question 45

What sites for ventriculostomy do you know?

Answer 45

Kocher's point - 11 cm from the nasion and 3 cm from midline Keen's point - 4cm above and behind the pinna Fraiser's point - 6cm above the inion and 3 cm lateral Dandy's point - 3 cm above the inion and 3 cm lateral

Question 46

What are the components of a shunt valve?

Answer 46

There is a differential pressure unit and a gravitational unit. The differential pressure can be fixed or adjustable and when the CSF pressure rises above the set pressure the valve opens and CSF drains. The mechanism usually involves a ruby with the pressure being dependent on a spring. Other designs involve silicon mitre, silicon slit valves and rubber diaphragm valves. There are also flow regulated devices. The gravitational unit can be fixed or adjustable and engages when the patient is upright to prevent a siphoning effect.

Question 47

How do flow regulated valves work?

Answer 47

They demonstrate a sigmoidal relation between pressure and flow by maintaining a fixed aperture through which CSF can flow meaning the flow remains relatively constant over a certain pressure range. Beyond maximum pressure, the maximum flow is reached and does not increase any further. The maximum flow is based on Poiseulle's law where the flow is proportional to the radius^4. The orbis sigma is one example and is useful when patients are volume drainage dependent and at risk of overdrainage.

Question 48

What are the ideal requirements of a shunt?

Answer 48

Outflow resistance should be the same as normal CSF outflow resistance (6-10 mmHg/ml/min). The flow should remain constant under constant pressure conditions and not be affected by body position Flow should be one-way Opening and closing pressures should remain constant Be free of blockage Be free of infection

Question 49

Describe how you would perform a resection of a convexity meningioma.

Answer 49

I would position an appropriately anaesthetised and consented patient supine in a Mayfield clamp with the head rotated to the contralateral side. I would employ neuronavigation to mark out the tumour and the required craniotomy and plan the skin incision based on this to best preserve the vascularity of the scalp. After craniotomy, I prefer to open the dura circumferentially around the base of the lesion. In line with Al-Mefty's 4D of meningioma surgery which includes De-dress, Devascularise, Debulk and Dissect. I would use an ultrasonic aspirator or monopolar cutting loops to debulk the lesion and dissect the margins but collapsing the capsule into the cavity taking care to preserve cortical veins. The dural tail with a 1 cm margin would be removed with the capsule and hyperostotic bone may need to be drilled or removed.

Question 50

What is the cause of headaches, unilateral visual loss and anosmia?

Answer 50

Foster-Kennedy syndrome = Anosmia, Optic atrophy and contralateral papilloedema. Associated with olfactory groove meningiomas.

Question 51

Describe how you would perform a resection of an olfactory groove meningioma.

Answer 51

I would place an appropriately consented and anaesthetized patient supine in a Mayfield clamp. I would utilise neuronavigation and perform a bicoronal (souttar incision) raising the skin flap forward and preserving a pericranial flap. I would then perform a bifrontal craniotomy, cranialise the frontal sinuses if breached and divide the superior sagittal sinus. I would then undertake subfrontal dissection to encounter the meningioma. I would then undertake an aggressive devascularisation along the base of the meningioma as the blood supply is from the anterior and posterior ethmoidal arteries before then internally debulking the lesion using a CUSA or cutting loops. I would then dissect the capsule from the brain interface collapsing the capsule into the cavity. At the back of the lesion, I would be mindful to identify and protect the anterior cerebral arteries as well as the optic apparatus, ICA and infundibulum in larger cases. An alternative for smaller lesions would be through a unilateral pterional approach or an extended endoscopic endonasal approach.

Question 52

Where do the anterior and posterior ethmoidal arteries enter the skull?

Answer 52

The anterior and posterior ethmoidal arteries are branches of the ophthalmic arteries and enter the skull as the junction of the cribiform plate (ethmoid bone) with the frontal bone.

Question 53

How do you decompress the optic nerves through a subfrontal approach?

Answer 53

The falciform ligament which forms the roof the optic canal and is continuous with the distal dural ring is incised and released.

Question 54

Label the anatomy of the sphenoid bone

Answer 54

Question 55

Describe the VFD

Answer 55

There is a bitemporal hemianopic defect which is also involving the inferior nasal quadrants bilaterally. This suggests that the compression is worse on top of the chiasm and is in keeping with a suprasellar mass pushing down on the chiasm and not a sellar mass pushing up. This would be consistent with a tuberculum sella meningioma.

Question 56

How would you resect a sphenoid wing meningioma?

Answer 56

I would place an appropriately consented and anaesthetised patient supine on the operating table in a Mayfield clamp with the head rotated 30-45 deg to the contralateral side with mild extension to aid temporal lobe retraction. I would fashion a pterional craniotomy through an curvilinear incision extending from the zygoma to widow's peak and taking care to drill down the greater wing of the sphenoid so that the middle and anterior fossae were flush. I would open the dura and reflect forwards with tacking sutures. Dissection of the proximal sylvian fissure would facilitate access to the tumour as well as allowing CSF egress to relax the brain. A lumbar drain would be useful for large meningiomas. A retractor system is used to hold the frontal lobe. I would devascularise the base and perform an internal debulking before careful dissection of the capsule wall, collapsing it into the cavity. I would be mindful to identify and protect the MCA, CN3 as well as the internal carotid artery. For medial sphenoid wing meningiomas an optic nerve decompression may also be needed.

Question 57

How do you deal with a parasagittal meningioma involving the sinus?

Answer 57

The Sindou classification separates these into those in which the meningioma involves the outer dura, infiltrate the sinus and completely occlude the sinus. Dedicated venous imaging is needed to assess the patency of the venous sinus and identification of cortical venous collaterals. In the case of involvement of the outer dura it may be possible to dissect this free. In cases of complete occlusion, it may be safe to sacrifice the sinus as venous collateralisation is likely to have occurred. For incomplete occlusion types, I would leave the sinus component and monitor this or treat it with SRS as appropriate.

Question 58

What are the excitation and emission spectra for the following fluorescence agents?

Answer 58

Fluoroscein excites at 490 and emits at 520 nM 5-ALA excites are 405 and emits at 625 nM ICG excites at 750 and emits at 800 nM

Question 59

What is 5ALA?

Answer 59

This is a precursor of protoprophyrin-9 which is part of the haem synthesis pathway within mitochondria. There is an abnormal breakdown in GBMs due to a reduction in the ferrochelatase enzyme resulting in a build-up of protoprophyrin-9 which is a fluorophore. Dose is 25mg/Kg given orally 4 hours prior to surgery.

Question 60

What are the corridors to the 3rd ventricle?

Answer 60

Trans-foramen of monre Transchoroidal (between the choroid plexus and fornix - taenia fornices) Interforniceal (split the septum pellucidum)

Question 61

How would you approach this lesion?

Answer 61

I would place an appropriately consented patient under general anaesthesia in a Mayfield clamp supine with the head neutral. I utilise neuronavigation to plan a craniotomy straddling the superior sagittal sinus at the level of the coronal suture. I would utilise a bicoronal (Soutar incision) and aim to place burr holes on either side of the midline and extending 5 cm laterally on the right side. I would then reflect the dural over the superior sagittal sinus and introduce the surgical microscope to undertake an interhemispheric transcallosal approach to the right ventricle. Once in the ventricle, I would orientate myself using the thalamostriate and septal veins as well as the choroid plexus and identify the foramen of Monroe, but this may be obscured by the lesion. If possible I would want to devascularise the lesion at the attachment to the choroid plexus as the vascular supply is from the anastomosis of the choroidal arteries. I would then debulk the lesion using a CUSA and resect the lesion in total. I would leave an EVD in situ for 24 hours.

Question 62

What approach would you use for a lesion in the atrium of the lateral ventricle?

Answer 62

A trans-interparietal sulcus (IPS) approach. This runs between the IPL and SPL and terminates in the postcentral sulcus. The intermediate sulcus of Jensen runs between the SMG and AnG. The sulcus of Brissaud runs perpendicular from the IPS into the SPL.

Question 63

What is the role of the superior parietal lobule?

Answer 63

This is a higher-order association cortex between sensory and visual information. Lesions result in astereoagnosis and neglect.

Question 64

Talk me through the principles of resecting this lesion.

Answer 64

The appearances are that of a midthoracic intradural extra-axial lesion arising from the ventral dura with broad dural attachment and is in keeping with a meningioma, but other possibilities include peripheral nerve sheath tumours (schwannomas and neurofibromas). This is a challenging case this represents a watershed area of the spine, the spinal cord is severely compressed and the lesion is ventral with the spinal cord draped over the back so impeding a direct posterior approach. I would utilise intraoperative neurophysiological monitoring with SEEPs and MEPs ensuring my anaesthetist did not give any long-acting paralytics. or halogenated anaesthetics. I would then take an appropriately consented and anaesthetised patient and position them prone on a montreal mattress. I would then gain an external level check through needle markings counting from the sacrum followed by fluoroscopy to reconfirm the levels. I would perform a midline thoracic incision and bilateral muscle strip. I would undertake an internal level check and perform a laminoplasty of the lamina above and below the lesion. In this case, there appears to be spinal cord on the dorsal surface making a posterior particularly challenging. A costrotransversectomy with drilling of the pedicles may also be required to facilitate access. I would then undertake an ultrasound before opening the dura. I would open the dura in the midline and hitch the leaves bilaterally. I would identify the superior and inferior margins. Thoracic nerve root sacrifice and release of the dentate ligament is required to facilitate gentle rotation of the cord. Resection is with a CUSA to debulk prior to capsule resection. After resection of the lesion attention should then be paid to reconstruction of the dura if this is to be resected. The risk of recurrence is significantly higher if this is the case. A lumbar drain should also be left in situ for 5 days.

Question 65

What is the recurrence rate of spinal meningiomas?

Answer 65

Over 95% of these are WHO grade 1. The literature gives wide ranges for this. In cases where the dura is resected and patched, the rates are around 10% at 5 years. In cases where the dura is not or cannot be resected such as in the large series by Klekamp and Samii, the recurrence rate is 20-40%.

Question 66

What are the principles of aneurysm surgery?

Answer 66

Positioning - to aid with gravity retraction of the brain and facilitate direct access to the aneurysm as well as for proximal control. Care is taken to prevent kinking of the neck veins which would result in venous congestion. Craniotomy - should be large enough to allow access for proximal control, to the aneurysm, to allow for brain swelling in ruptured cases and potential post-operative swelling. The sphenoid wing should be drilled flat to minimise brain retraction. CSF drainage - shoulder be performed early to allow adequate brain relaxation along with liberal arachnoid dissection. This can be performed through an EVD if present or after the craniotomy via Paine's point. Superficial clot evacuation would aid with brain relaxation. Retractors - should be used to hold the brain and not to apply undue force. Proximal control - and occlusion with a temporary clip in case of rupture is essential. Clipping - avoid perforator and distal vessel occlusion e.g. Heubner Intraoperative doppler / ICG are useful to confirm exclusion of the aneurysm from the circulation as well as patency and flow in the distal branches.

Question 67

What is the dose of ICG?

Answer 67

Max dose 2 mg/Kg Reconstitute 50mg in 50ml and give 5-10 ml with a 10 ml flush. For a 70 Kg patient this can be repeated up to 10-20 times.

Question 68

What are the principles of intrinsic glioma surgery?

Answer 68

Neuronavigation - lesion, vascular anatomy (sinus) localisation. Craniotomy and skin flap planning. Awake craniotomy for electrophysiological mapping (motor and language). Motor mapping can also be undertaken asleep. Cortical stimulation with monopolar and bipolar probes. Subcortical mapping with Raabe suction monopolar probe. Start at 10mA and reduce down to 5mA = 5 mm from tract. Ultrasound / iMRI to aid with complete surgical resection 5-ALA - precursor or protoporphyrin 9. Excitation at 405 and emission at 625 nM. Gliadel / Carmustine wafers are an option if \>90% of the tumour has been resected. Contraindicated if the ventricles are open. Dural closure is important. Risk of impaired wound healing.

Question 69

What are the principles of AVM resection?

Answer 69

Pre-operative planning - review the DSA with the neuroradiologist to understand the angioarchitecture of the nidus. Any high-risk features such as nidal aneurysms should be treated endovascularly if possible. Identification of the main draining vein as well as the feeding artery supply. All of the different angiographic runs will show the contributions from different vascular territories. It is important to identify the deep arterial supply. Similarly, for the venous drainage, this should be maintained until the entire AVM is devascularised. En-passage feeders should be carefully skeletonised to prevent ischaemic injury. Nidus location - consideration is given to the region of eloquence, presence of a haematoma cavity and pre-existing neurological deficit. Persistant bleeding from the cavity suggests a residual nidus.

Question 70

How do you manage a torn sinus during surgery?

Answer 70

I would immediately cover the bleeding site with wet gauze and flood the field with saline to prevent an air embolus. I would then inform the anaesthetist that I have a significant haemorrhage and that blood products would be required. I would then ask the anaeshetist to slowly elevate the head of the bed to minimise the bleeding to a rate where the site can be identified being careful to continuously irrigate the site to prevent air embolism. If the sinus is torn consideration is then given to how this can be repaired. In the first instance haemostatic products should be used such as surgicel (oxidised cellulose), surgiflow (gelatin granules with thrombin, or haemopatch (cellulose pad with polyethylene glycol). If these techniques do not work then consideration should be given to either suturing the dural ends or flapping the dura over the defect and suturing this down to reconstruct the sinus wall.

Question 71

Interpret the audiogram

Answer 71

There is a right-sided sensorineural hearing deficit as there is no difference between air and bone conduction. Masking has been employed when testing the air and bone conduction to prevent crossover of sound from one ear to the other. Masked bone conduction has also been applied. Masking is performed by applying noise to the non-test ear.

Question 72

What are the degrees of hearing loss?

Answer 72

Normal 0-20 dB Mild 20-40 dB Moderate 40-55 dB Moderately-Severe 55-70 dB Severe 70-90 dB Profound \>90 dB

Question 73

What is the Gardner Robertson classification of hearing loss?

Answer 73

1 = Good: \<30 dB PTA and \>70 Speech discrimination 2 = Serviceable: 30-50 dB PTA and 50-70 Speech discrimination 3 = Non-servicable: 50-90 dB PTA and 5-50 Speech discrimination 4 = Poor: \>90 PTA and \<5 Speech discrimination 5 = Deaf

Question 74

How do you manage intraoperative swelling?

Answer 74

Elevate the head Prevent any occlusion of venous return Optimise anaesthetic parameters: pCO2, p02, sedation and hyperosmolar therapies e.g. mannitol (0.5-1g/kg) / hypertonic saline (2-4 ml/kg) CSF drainage Identify/evacuate any haematoma formation

Question 75

What are the principles of stereotaxy?

Answer 75

Stereotaxy is the ability to accurately place instruments within the brain based on a 3D coordinate system. Stereo = 3D space Taxy = to touch.

Question 76

What are the considerations prior to placement of a stereotactic frame?

Answer 76

Sites of shunts and tubing Previous craniotomy and burr hole sites Supine or lateral position

Question 77

How do you place a stereotactic frame?

Answer 77

I first check to see if there are any shunts or if the patient has had a previous craniotomy or craniectomy. I then construct the frame ensuring the faceplate attachment is anterior with long posts and the posterior posts are shorter. I then use a frame holder and stack gauze at the top of the head until the frame is parallel to the zygoma and ask an assistant to hold it there whilst I apply local anaesthetic along the trajectory of the screw. An alternative is to use ear bars but I find patients find this uncomfortable. The distance from the scalp to the frame is then measured and appropriately sized screws are selected. These are tightened at opposite angles until sufficient bone purchase is achieved. The fiducial box is then placed and the patient undergoes an MRI or CT scan.

Question 78

How does the Leksell frame coordinate system work?

Answer 78

The Leksell frame has an arc, radius of which is 190 mm and the stereotactic frame is designated through a Cartesian coordinate system with the centre at 100 mm at X, Y and Z. 0 is by convention right, posterior and superior. The fiducial box is fixed to the frame scanned orthogonally to the scanner table. The centre of the frame (x=100 and y=100) is determined by the intersection of the lines drawn from the corners of the localising frame. The N-shaped localiser contains copper sulphate which returns high signal on MRI.

Question 79

What is the Engel classification for seizure outcome?

Answer 79

Class 1 = Free of disabling seizures (equivalent to ILAE 1-3). Class 2 = Rare disabiling seizures Class 3 = Worthwhile reduction Class 4 = No worthwhile reduction

Question 80

What is the ILAE seizure outcome?

Answer 80

Class 1: Completely seizure-free; no auras Class 2: Only auras; no other seizures Class 3: 1 to 3 seizure days per year; ± auras Class 4: 4 seizure days per year to 50% reduction of baseline seizure days; ± auras Class 5: Less than 50% reduction of baseline seizure days; ± auras Class 6: More than 100% increase of baseline seizure days; ± auras

Question 81

What is spasticity?

Answer 81

A velocity-dependent increase in tone in response to passive stretch

Question 82

How is spasticity graded?

Answer 82

0-4 0 = no increase in tone 4 = Rigid in flexion or extension

Question 83

What are the treatment options for spasticity?

Answer 83

Diazepam Baclofen Botox injection Intrathecal baclofen pumps SDR Peripheral neurectomy Orthopaedic tendon releases

Question 84

What are the causes of a peripheral neuropathy?

Answer 84

ABCDEFG Alcohol / Amyloid / AIDS B12 def CIDP / Connective tissue disease DM / Drugs Entrapment /Endocrine GBS Hereditary Infection

Question 85

How you classify peripheral nerve injuries?

Answer 85

Seddon classification: Neuropraxia - conduction block due to Wallerian degeneration Axontomesis - Nerve intact but axons not in continuity. Neurotmesis - Nerve not intact. Recovery requires surgical intervention.

Question 86

The differential of an extra-axial mass in the cranium and spine?

Answer 86

Cranium - meningioma, haemangiopericytoma, metastasis, arachnoid cyst, epidermoid, schwannoma Spine - Meningioma, neurofibroma, schwannoma, ependymoma

Question 87

What is this lesion?

Answer 87

Pilocytic astrocytoma - most commonly in the cerebellar hemisphere. FLAIR shows a cystic lesion with a mural nodule. No surrounding oedema. Mass effect on the 4th ventricle results in obstructive hydrocephalus. The differential would include a haemangioblastoma, medulloblastoma, ependymoma and ganglioglioma.

Question 88

What is this lesion?

Answer 88

CT axial image through the posterior fossa shows a solid and cystic mass causing obstructive hydrocephalus. There is supratentorial hydrocephalusus. The isodensity of the solid component is in keeping with a pilocytic astrocytoma. I would expect medulloblastomas to be more hyperdense.

Question 89

What is this lesion?

Answer 89

A hypothalamic / optic pathway glioma. Coronal T2: This is a large lesion with no surrounding oedema. 1/3 of patients with OPGs have NF1. Differential includes a pilomyxoid astrocytoma, ADEM, tumefactive MS, hypothalamic hamartoma.

Question 90

What are the histological features of a pilocytic astrocytoma?

Answer 90

Compact bipolar cells with Rosenthal fibres. Loose reticulate astrocytes with microcysts. Highly vascular with glomeruloid tufts. MIB-1 1% GFAP+, IDH-1WT

Question 91

What is the usual age range for pilocytic astrocytomas?

Answer 91

80% less than 20 years.

Question 92

What are these tumours in a child?

Answer 92

Supratentorial cyst with an enhancing nodule in a child is most likely a pilocytic astrocytoma. Other differentials include PXA, ganglioglioma (cortical and enhances) and DNET (no enhancement)

Question 93

What is this lesion?

Answer 93

OPG - the enhancement pattern is variable. 1/3 of patients will have NF1.

Question 94

What is this lesion?

Answer 94

The T2 image reveals a large H-shaped mass centred on the hypothalamus/chiasmatic region. It is well circumscribed with no oedema. The diagnosis is a pilomyxoid astrocytoma. The differential is an OPG (pilocytic astrocytoma) or craniopharyngioma.

Question 95

What is the histology?

Answer 95

There are bipolar pilocytic cells wth no Rosenthal fibres. There is mucin stain (blue) showing a mucinous matrix with embedded glial cells. This is a pilomyxoid astrocytoma.

Question 96

What is this lesion?

Answer 96

PXA (WHO grade 2) - these arise from SUBPIAL ASTROCYTES A cortical lesion with solid contrast enhancing component in a child. Cystic component displacing the brainstem. The histological section reveals nuclear pleomorphism with multinucleated giant cells and vacuolation.

Question 97

What is this lesion in a child?

Answer 97

The CT shows a contrast enhancing lesion with in the latearl ventricle adjacent to the foramen of Monroe causing entrapment of the left lateral ventricle as evidenced by the ventriculomegaly and periventricular oedema. There is an associated hypodensity which most likely represents a cortical tuber. The FLAIR confirms a complex heterogenous lesion at the forame of Monroe. There is a left posterior temporal cortical tuber and right frontal subcortical hyperintensity indicative of a focal cortical dysplasia. The child has tuberous sclerosis. Differential includes a central neurocytoma, intraventricular meningioma, choroid plexus papilloma, astrocytoma arising from the septum pellucidum and an ATRT.

Question 98

What are the imaging characteristics of oligodendrogliomas?

Answer 98

Cortical subcortical lesions that are heterogenous with solid and cystic components. There is deep infiltration and calvarial remodelling may occur. 90% show calcification on CT. FLAIR shows significant surrounding oedema with cortical and subcortical involvement. T1WI shows heterogenous enhancement.

Question 99

What is this lesion?

Answer 99

Age 20-40 years Well circumscribed lesion arising from the septum pellucidum causing compression of the foramen of Monroe bilaterally. The MRI shows prominent flow voids and diffuse heterogeneous enhancement. Differential includes a meningioma, SEGA, choroid plexus papilloma and astrocytoma.

Question 100

Describe the SINS score.

Answer 100

The spinal instability in neoplasia score is based on: Location (Junctional, Mobile, Semi rigid and Rigid) Posterior lateral involvement Sclerotic / blastic mets % of VD involved Collapse \>50% or less than 50% Deformity Mechanical pain

Question 101

What are the theories of syrinx formation in Chiari 1 malformation?

Answer 101

Gardner's waterhammer theory suggests that obstruction to csf flow across the CCJ results in CSF transmission through the obex and result in syrinx formation. Ball and Dylan suggested that CSF is forced into perivascular / Virchow Robin spaces. Oldfield suggested that the tonsils act like pistons transmitting pressure waves into the central canal. William's suck and slosh theory (similar mechanism)